It has been reported from Ummi Salamah Radhiyallahu 'Anha:
"Rasulullah Sallallahu 'Alayhi Wasallam preferred wearing, from among all clothing, the qamis (thowb)" (RU)
English reference (RU): Book 8, Hadith 55 (RU)
Arabic reference (RU): Book 8, Hadith 56 (RU)